Conversion of oxygenates to olefins

ABSTRACT

A process is described for converting an oxygenate-containing feedstock into one or more olefins in a reactor system including a plurality of fixed bed reactors each containing a catalyst composition comprising a molecular sieve and at least one metal oxide having an uptake of carbon dioxide at 100° C. of at least 0.03 mg/m 2  of the metal oxide. Each reactor is sequentially rotated between at least one operating mode, wherein the catalyst composition in the reactor is contacted with the oxygenate-containing feedstock, and a regeneration mode, wherein the catalyst composition in the reactor is contacted with a regeneration medium.

FIELD OF INVENTION

This invention relates to a method for catalytically converting a feedincluding an oxygenated hydrocarbon to a light olefin product in a fixedbed reactor system.

BACKGROUND

Light olefins, such as ethylene, propylene, butylenes and mixturesthereof, serve as feeds for the production of numerous importantchemicals and polymers. Typically, C₂-C₄ light olefins are produced bycracking petroleum refinery streams, such as C₃+ paraffinic feeds. Inview of limited supply of competitive petroleum feeds, production of lowcost light olefins from petroleum feeds are subject to waning supplies.Efforts to develop light olefin production technologies based onalternative feeds have therefore increased.

An important type of alternative feed for the production of lightolefins is oxygenates, such as C₁-C₄ alkanols, especially methanol andethanol; C₂-C₄ dialkyl ethers, especially dimethyl ether (DME), methylethyl ether and diethyl ether; dimethyl carbonate and methyl formate,and mixtures thereof. Many of these oxygenates may be produced fromalternative sources by fermentation, or from synthesis gas derived fromnatural gas, petroleum liquids, carbonaceous materials, including coal,recycled plastics, municipal wastes, or any organic material. Because ofthe wide variety of sources, alcohol, alcohol derivatives, and otheroxygenates have promise as economical, non-petroleum sources for lightolefin production.

The preferred process for converting an oxygenate feedstock, such asmethanol, into one or more olefin(s), primarily ethylene and/orpropylene, involves contacting the feedstock with a molecular sievecatalyst composition. Molecular sieves are porous solids having pores ofdifferent sizes, such as zeolites or zeolite-type molecular sieves,carbons and oxides. The most commercially useful molecular sieves forthe petroleum and petrochemical industries are zeolites, for examplealuminosilicate molecular sieves. Zeolites in general have a one-, two-or three-dimensional crystalline pore structure having uniformly sizedpores of molecular dimensions that selectively adsorb molecules that canenter the pores, and exclude those molecules that are too large.

There are many different types of molecular sieve well known to converta feedstock, especially an oxygenate containing feedstock, into one ormore olefin(s). For example, U.S. Pat. No. 5,367,100 describes the useof the zeolite, ZSM-5, to convert methanol into olefin(s); U.S. Pat. No.4,062,905 discusses the conversion of methanol and other oxygenates toethylene and propylene using crystalline aluminosilicate zeolites, forexample Zeolite T, ZK5, erionite and chabazite; U.S. Pat. No. 4,079,095describes the use of ZSM-34 to convert methanol to hydrocarbon productssuch as ethylene and propylene; and U.S. Pat. No. 4,310,440 describesproducing light olefin(s) from an alcohol using a crystallinealuminophosphate, often designated AlPO₄.

Some of the most useful molecular sieves for converting methanol toolefin(s) are silicoaluminophosphate molecular sieves.Silicoaluminophosphate (SAPO) molecular sieves contain athree-dimensional microporous crystalline framework structure of [SiO₄],[AlO₄] and [PO₄] corner sharing tetrahedral units. SAPO synthesis isdescribed in U.S. Pat. No. 4,440,871, which is herein fully incorporatedby reference. SAPO molecular sieves are generally synthesized by thehydrothermal crystallization of a reaction mixture of silicon-,aluminum- and phosphorus-sources and at least one templating agent.Synthesis of a SAPO molecular sieve, its formulation into a SAPOcatalyst, and its use in converting a hydrocarbon feedstock intoolefin(s), particularly where the feedstock is methanol, are disclosedin U.S. Pat. Nos. 4,499,327, 4,677,242, 4,677,243, 4,873,390, 5,095,163,5,714,662 and 6,166,282, all of which are herein fully incorporated byreference.

Conversion of oxygenates to olefins generates and deposits carbonaceousmaterial (coke) on the molecular sieve catalysts used to catalyze theconversion process. Over-accumulation of these carbonaceous depositswill inhibit the catalyst's ability to promote the reaction. In order toavoid unwanted build-up of coke on the molecular sieve catalyst, theoxygenate to olefin process generally incorporates a second stepcomprising catalyst regeneration. During regeneration, the coke isremoved from the catalyst, typically by combustion with oxygen, which atleast partially restores the catalytic activity of the catalyst. Theregenerated catalyst then may be reused to catalyze the conversion ofoxygenates to olefins.

For example, SAPO-34 is known to be a selective molecular sieve catalystin the conversion of methanol to ethylene and propylene. However, itsexcellent selectivity to ethylene and propylene (maximum selectivityabout 40-43 wt % each) requires the formation of a carbon pool ascarbonaceous material is being deposited on the catalyst. With freshcatalyst, ethylene and propylene selectivities are about 20-24 wt % andabout 32-36 wt % respectively rising to their maximum values with timeas more carbonaceous material is being deposited. However, catalystactivity drops off rapidly when the carbonaceous material is greaterthan about 10 wt % (based on SAPO-34 molecular sieve content). Fixed bedoperation is not practical since catalyst life under a reasonable spacevelocity (at least 3 w/w/hr) is less than 2.5 hours. For this reasonmost current proposals for converting oxygenates to olefins employ afluidized bed reactor in which the catalyst is continuously circulatedbetween a riser reactor and a regenerator.

It would, however, be desirable to provide an improved molecular sievecatalyst composition and process which would enable a fixed bed reactorsystem to be employed in an economically viable manner in the conversionof oxygenates, such as methanol, to olefins.

U.S. Pat. No. 4,873,390 to Lewis et al., incorporated herein byreference, teaches conversion of a feedstock, e.g., alcohols, to aproduct containing light olefins over a silicoaluminophosphate catalysthaving pores with a diameter of less than 5 Angstroms, wherein acarbonaceous deposit material is formed on the catalyst. The catalyst istreated to form a partially regenerated catalyst having from 2 to 30 wt.% of the carbonaceous deposit material. The catalyst is preferably in afluidized state and is continuously transported between the reactionzone and the regeneration zone.

U.S. Pat. No. 6,023,005 to Lattner et al., incorporated herein byreference, discloses a method of producing ethylene and propylene bycatalytic conversion of oxygenate in a fluidized bed reaction processwhich utilizes catalyst regeneration. The process maintains a portion ofdesired carbonaceous deposits on the catalyst by removing only a portionof the total reaction volume of coked molecular sieve catalyst andregenerating only that portion of catalyst, which is then mixed backwith the unregenerated remainder of catalyst. The resulting catalystmixture contains 2-30 wt % carbonaceous deposits.

In our co-pending U.S. Patent Publication No. 2003/0176752 publishedSep. 18, 2003, incorporated herein by reference, there is described acatalyst composition that exhibits enhanced lifetime when used in theconversion of oxygenates to olefins and which comprises a molecularsieve and at least one metal oxide having an uptake of carbon dioxide at100° C. of at least 0.03 mg/m² of the metal oxide. The metal oxide isselected from an oxide of Group 4 of the Periodic Table of Elements,either alone or in combination with an oxide selected from Group 2 ofthe Periodic Table of Elements and/or an oxide selected from Group 3 ofthe Periodic Table of Elements, including the Lanthanide series ofelements and the Actinide series of elements.

In our co-pending U.S. Patent Publication No. 2003/0176753 publishedSep. 18, 2003, incorporated herein by reference, there is described acatalyst composition that exhibits enhanced lifetime when used in theconversion of oxygenates to olefins and which comprises a molecularsieve and at least one metal oxide having an uptake of carbon dioxide at100° C. of at least 0.03 mg/m² of the metal oxide. The metal oxide isselected from an oxide of a metal from Group 3 of the Periodic Table ofElements, the Lanthanide series of elements and the Actinide series ofelements.

U.S. Pat. No. 4,789,528 to Owen et al., incorporated herein byreference, teaches a multi-reactor system for the conversion of lightolefins to gasoline and/or distillate in which at least three reactorsare sequentially rotated between a regeneration mode and at least twoserially connected reaction modes respectively. In the reaction modes,the reactor having relatively less fresh catalyst receives feed from afeed source first and the reactor having the fresher catalyst receivesthe feed last.

SUMMARY

The present invention relates to a process for converting anoxygenate-containing feedstock into one or more olefins in a reactorsystem including a plurality of fixed bed reactors each containing acatalyst composition comprising a molecular sieve and at least one metaloxide having an uptake of carbon dioxide at 100° C. of at least 0.03mg/m² of the metal oxide, wherein each reactor is sequentially rotatedbetween at least one operating mode, wherein the catalyst composition inthe reactor is contacted with the oxygenate-containing feedstock, and aregeneration mode, wherein the catalyst composition in the reactor iscontacted with a regeneration medium.

In one embodiment, the reactor system comprises at least three of saidfixed bed reactors and each reactor is sequentially rotated from saidregeneration mode to a first operating mode, then to at least a secondoperating mode and then back to said regeneration mode, wherein reactorsin said first and second operating modes are connected in series suchthat the oxygenate-containing feedstock contacts the catalystcomposition in a reactor in the second operating mode before contactingthe catalyst composition in a reactor in the first operating mode.

Conveniently, the metal of said at least one metal oxide is selectedfrom Group 2, Group 3 (including the Lanthanide and Actinide seriesmetals) and Group 4 of the Periodic Table of Elements using the IUPACformat described in the CRC Handbook of Chemistry and Physics, 78thEdition, CRC Press, Boca Raton, Fla. (1997). For example, the metaloxide may be selected from zirconium oxide, hafnium oxide, magnesiumoxide, calcium oxide, barium oxide, lanthanum oxide, yttrium oxide,scandium oxide, cerium oxide, and mixtures thereof.

Conveniently, the catalyst composition also includes at least one of abinder and a matrix material different from the metal oxide.

In one embodiment, the molecular sieve comprises a framework includingat least two tetrahedral units selected from [SiO₄], [AlO₄] and [PO₄]units, such as a silicoaluminophosphate.

In a preferred embodiment, the present invention employs a molecularsieve which has a pore diameter of less than 5.0 Angstroms, e.g., amolecular sieve having a framework-type selected from AEI, AFT, APC,ATN, ATT, ATV, AWW, BIK, CAS, CHA, CHI, DAC, DDR, EDI, ERI, GOO, KFI,LEV, LOV, LTA, MON, PAU, PHI, RHO, ROG, THO, and substituted formsthereof. For example, the molecular sieve may be selected from ALPO-18,ALPO-34, SAPO-17, SAPO-18, and SAPO-34.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph illustrating the decrease in methanol conversion withtime on stream for a catalyst composition comprising SAPO-34 molecularsieve and varying amounts of La/ZrO₂.

FIG. 2 is a graph illustrating the extended lifetime for methanolconversion for a catalyst composition comprising SAPO-34 molecular sieveand yttrium oxide.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Introduction

The present invention provides a process for converting anoxygenate-containing feedstock into one or more olefins in a reactorsystem which includes a plurality of fixed bed reactors. Each of thefixed bed reactors contains a catalyst composition comprising amolecular sieve and at least one metal oxide having an uptake of carbondioxide at 100° C. of at least 0.03 mg/m² of the metal oxide. Inparticular, it has been found that combining a molecular sieve with sucha metal oxide results in a marked increase in the lifetime of thecatalyst composition when used in the conversion of oxygenates intoolefins. As a result, it has for the first time become feasible toconduct the conversion process in a multi-reactor system wherein eachreactor is sequentially rotated between at least one operating mode,wherein the catalyst composition in the reactor is contacted with theoxygenate-containing feedstock, and a regeneration mode, wherein thecatalyst composition in the reactor is contacted with a regenerationmedium.

In one practical embodiment, the reactor system includes three or morefixed bed reactors that can be sequentially rotated from saidregeneration mode through a plurality of operating modes and then backto said regeneration mode. When in the operating modes, the reactors areconnected in series such that the reactor containing the most recentlyregenerated (i.e., most active) catalyst contacts theoxygenate-containing feedstock last and the reactor containing the leastrecently regenerated (i.e., most aged) catalyst contacts theoxygenate-containing feedstock first.

Molecular Sieves

Molecular sieves have been classified by the Structure Commission of theInternational Zeolite Association according to the rules of the IUPACCommission on Zeolite Nomenclature. According to this classification,framework-type zeolite and zeolite-type molecular sieves, for which astructure has been established, are assigned a three letter code and aredescribed in the Atlas of Zeolite Framework Types, 5th edition,Elsevier, London, England (2001), which is herein fully incorporated byreference.

Crystalline molecular sieves all have a 3-dimensional, four-connectedframework structure of corner-sharing [TO₄] tetrahedra, where T is anytetrahedrally coordinated cation. Molecular sieves are typicallydescribed in terms of the size of the ring that defines a pore, wherethe size is based on the number of T atoms in the ring. Otherframework-type characteristics include the arrangement of rings thatform a cage, and when present, the dimension of channels, and the spacesbetween the cages. See van Bekkum, et al., Introduction to ZeoliteScience and Practice, Second Completely Revised and Expanded Edition,Volume 137, pages 1-67, Elsevier Science, B.V., Amsterdam, Netherlands(2001).

Non-limiting examples of molecular sieves are the small pore molecularsieves, AEI, AFT, APC, ATN, ATT, ATV, AWW, BIK, CAS, CHA, CHI, DAC, DDR,EDI, ERI, GOO, KFI, LEV, LOV, LTA, MON, PAU, PHI, RHO, ROG, THO, andsubstituted forms thereof, the medium pore molecular sieves, AFO, AEL,EUO, HEU, FER, MEL, MFI, MTW, MTT, TON, and substituted forms thereof;and the large pore molecular sieves, EMT, FAU, and substituted formsthereof. Other molecular sieves include ANA, BEA, CFI, CLO, DON, GIS,LTL, MER, MOR, MWW and SOD. Non-limiting examples of preferred molecularsieves, particularly for converting an oxygenate containing feedstockinto olefin(s), include AEL, AFY, AEI, BEA, CHA, EDI, FAU, FER, GIS,LTA, LTL, MER, MFI, MOR, MTT, MWW, TAM and TON. In one preferredembodiment, the molecular sieve used in the present process has an AEItopology or a CHA topology, or a combination thereof, most preferably aCHA topology.

The small, medium and large pore molecular sieves have from a 4-ring toa 12-ring or greater framework-type. In a preferred embodiment, themolecular sieves have 8-, 10- or 12-ring structures and an average poresize in the range of from about 3 Å to 15 Å. In a more preferredembodiment, the molecular sieves, preferably silicoaluminophosphatemolecular sieves, have 8-rings and an average pore size less than about5 Å, such as in the range of from 3 Å to about 5 Å, for example from 3 Åto about 4.5 Å, and particularly from 3.5 Å to about 4.2 Å.

Molecular sieves have a molecular framework of one, preferably two ormore corner-sharing [TO₄] tetrahedral units, more preferably, two ormore [SiO₄], [AlO₄] and/or [PO₄] tetrahedral units, and most preferably[SiO₄], [AlO₄] and [PO₄] tetrahedral units. These silicon, aluminum, andphosphorus based molecular sieves and metal containing derivativesthereof have been described in detail in numerous publications includingfor example, R. Szostak, Handbook of Molecular Sieves, Van NostrandReinhold, New York, N.Y. (1992), which is herein fully incorporated byreference.

The more preferred molecular sieves include aluminophosphate (AlPO)molecular sieves and silicoaluminophosphate (SAPO) molecular sieves andsubstituted, preferably metal substituted, AlPO and SAPO molecularsieves. The most preferred molecular sieves are SAPO molecular sieves,and metal substituted SAPO molecular sieves. In an embodiment, the metalis an alkali metal of Group 1 of the Periodic Table of Elements, analkaline earth metal of Group 2 of the Periodic Table of Elements, arare earth metal of Group 3 of the Periodic Table of Elements, includingthe Lanthanides: lanthanum, cerium, praseodymium, neodymium, samarium,europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium,ytterbium and lutetium; and scandium or yttrium, a transition metal ofGroups 4 to 12 of the Periodic Table of Elements, or mixtures of any ofthese metal species. In one preferred embodiment, the metal is selectedfrom the group consisting of Co, Cr, Cu, Fe, Ga, Ge, Mg, Mn, Ni, Sn, Ti,Zn and Zr, and mixtures thereof. In another preferred embodiment, thesemetal atoms discussed above are inserted into the framework of amolecular sieve through a tetrahedral unit, such as [MeO₂], and carry anet charge depending on the valence state of the metal substituent. Forexample, in one embodiment, when the metal substituent has a valencestate of +2, +3, +4, +5, or +6, the net charge of the tetrahedral unitis between −2 and +2.

In one embodiment, the molecular sieve, as described in many of the U.S.Patents mentioned above, is represented by the empirical formula, on ananhydrous basis:mR:(M_(x)Al_(y)P_(z))O₂wherein R represents at least one templating agent, preferably anorganic templating agent; m is the number of moles of R per mole of(M_(x)Al_(y)P_(z))O₂ and has a value from 0 to 1, preferably 0 to 0.5,and most preferably from 0 to 0.3; x, y, and z represent the molefraction of Al, P and M as tetrahedral oxides, where M is a metalselected from one of Groups 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13,14 and Lanthanide's of the Periodic Table of Elements, preferably M isselected from one of the group consisting of Si, Co, Cr, Cu, Fe, Ga, Ge,Mg, Mn, Ni, Sn, Ti, Zn and Zr. In an embodiment, m is greater than orequal to 0.2, and x, y and z are greater than or equal to 0.01. Inanother embodiment, m is greater than 0.1 to about 1, x is greater than0 to about 0.25, y is in the range of from 0.4 to 0.5, and z is in therange of from 0.25 to 0.5, more preferably m is from 0.15 to 0.7, x isfrom 0.01 to 0.2, y is from 0.4 to 0.5, and z is from 0.3 to 0.5.

Non-limiting examples of SAPO and AlPO molecular sieves useful hereininclude one or a combination of SAPO-5, SAPO-8, SAPO-11, SAPO-16,SAPO-17, SAPO-18, SAPO-20, SAPO-31, SAPO-34, SAPO-35, SAPO-36, SAPO-37,SAPO-40, SAPO-41, SAPO-42, SAPO-44 (U.S. Pat. No. 6,162,415), SAPO-47,SAPO-56, AlPO-5, AlPO-11, AlPO-18, AlPO-31, AlPO-34, AlPO-36, AlPO-37,AlPO-46, and metal containing molecular sieves thereof. Of these,particularly useful molecular sieves are one or a combination ofSAPO-18, SAPO-34, SAPO-35, SAPO-44, SAPO-56, AlPO-18 and AlPO-34 andmetal containing derivatives thereof, such as one or a combination ofSAPO-18, SAPO-34, AlPO-34 and AlPO-18, and metal containing derivativesthereof, and especially one or a combination of SAPO-34 and AlPO-18, andmetal containing derivatives thereof.

In an embodiment, the molecular sieve is an intergrowth material havingtwo or more distinct crystalline phases within one molecular sievecomposition. In particular, intergrowth molecular sieves are describedin the U.S. Patent Application Publication No. 2002/0165089 andInternational Publication No. WO 98/15496 published Apr. 16, 1998, bothof which are herein fully incorporated by reference. For example,SAPO-18, AlPO-18 and RUW-18 have an AEI framework-type, and SAPO-34 hasa CHA framework-type. Thus the molecular sieve used herein may compriseat least one intergrowth phase of AEI and CHA framework-types,especially where the ratio of CHA framework-type to AEI framework-type,as determined by the DIFFaX method disclosed in U.S. Patent ApplicationPublication No. 2002/0165089, is greater than 1:1.

The preferred molecular sieves useful herein for oxygenates to olefinsconversion are synthesized by techniques well-known to those skilled inthe art, as described in many of the references discussed above.

Metal Oxides

Metal oxides useful herein are those metal oxides, different fromtypical binders and/or matrix materials, that, when used in combinationwith a molecular sieve in a catalyst composition, are effective inextending of the useful life of the catalyst composition in theconversion of oxygenates to olefins. Quantification of the extension incatalyst life is determined by the Lifetime Enhancement Index (LEI) asdefined by the following equation:${LEI} = \frac{{Lifetime}\quad{of}\quad{Catalyst}\quad{in}\quad{Combination}\quad{with}\quad{Active}\quad{Metal}\quad{Oxide}}{{Lifetime}\quad{of}\quad{Catalyst}}$where the lifetime of the catalyst or catalyst composition is thecumulative amount of oxygenate feedstock processed per gram of catalystcomposition until the conversion of the oxygenate feedstock by thecatalyst composition falls below some defined level, for example 10%. Aninactive metal oxide will have little to no effect on the lifetime ofthe catalyst composition, or will shorten the lifetime of the catalystcomposition, and will therefore have a LEI less than or equal to 1. Thusactive metal oxides of the invention are those metal oxides, differentfrom typical binders and/or matrix materials, that, when used incombination with a molecular sieve, provide a molecular sieve catalystcomposition that has a LEI greater than 1. By definition, a molecularsieve catalyst composition that has not been combined with an activemetal oxide will have a LEI equal to 1.0.

In particular, the metal oxides useful herein have an uptake of carbondioxide at 100° C. of at least 0.03 mg/m² of the metal oxide, such as atleast 0.035 mg/m² of the metal oxide. Although the upper limit on thecarbon dioxide uptake of the metal oxide is not critical, in general themetal oxides useful herein will have a carbon dioxide at 100° C. of lessthan 10 mg/m² of the metal oxide, such as less than 5 mg/m² of the metaloxide. Typically, the metal oxides useful herein have a carbon dioxideuptake of 0.04 to 0.2 mg/m² of the metal oxide.

In order to determine the carbon dioxide uptake of a metal oxide, thefollowing procedure is adopted. A sample of the metal oxide isdehydrated by heating the sample to about 200° C. to 500° C. in flowingair until a constant weight, the “dry weight”, is obtained. Thetemperature of the sample is then reduced to 100° C. and carbon dioxideis passed over the sample, either continuously or in pulses, again untilconstant weight is obtained. The increase in weight of the sample interms of mg/mg of the sample based on the dry weight of the sample isthe amount of adsorbed carbon dioxide.

In the Examples reported below, the carbon dioxide adsorption ismeasured using a Mettler TGA/SDTA 851 thermogravimetric analysis systemunder ambient pressure. The metal oxide sample is dehydrated in flowingair to about 500° C. for one hour. The temperature of the sample is thenreduced in flowing helium to 100° C. After the sample has equilibratedat the desired adsorption temperature in flowing helium, the sample issubjected to 20 separate pulses (about 12 seconds/pulse) of a gaseousmixture comprising 10 weight % carbon dioxide with the remainder beinghelium. After each pulse of the adsorbing gas the metal oxide sample isflushed with flowing helium for 3 minutes. The increase in weight of thesample in terms of mg/mg adsorbent based on the adsorbent weight aftertreatment at 500° C. is the amount of adsorbed carbon dioxide. Thesurface area of the sample is measured in accordance with the method ofBrunauer, Emmett, and Teller (BET) published as ASTM D 3663 to providethe carbon dioxide uptake in terms of mg carbon dioxide/m² of the metaloxide.

Suitable metal oxides include those metal oxides having a Group 4 metal,such as zirconium and/or hafnium, a Group 2 metal, such as magnesium,calcium, strontium and barium and/or a Group 3 metal (including theLanthanides and Actinides), such as yttrium, scandium, lanthanum, andcerium. In general, oxides of silicon, aluminum, and combinationsthereof are not preferred.

It is found that, by including an active metal oxide in combination witha molecular sieve, a catalyst composition can be produced having an LEIin the range of from greater than 1 to 2000, such as from about 1.5 toabout 1000. Typically catalyst compositions according to the inventionexhibit LEI values greater than 1.1, for example greater than 1.2, andmore particularly greater than 1.3, such as greater than 1.5, such asgreater than 1.7, such as greater than 2.

In one embodiment, the active metal oxide(s) has a BET surface area ofgreater than 10 m²/g, such as greater than 10 m²/g to about 300 m²/g. Inanother embodiment, the active metal oxide(s) has a BET surface areagreater than 20 m²/g, such as from 20 m²/g to 250 m²/g. In yet anotherembodiment, the active metal oxide(s) has a BET surface area greaterthan 25 m²/g, such as from 25 m²/g to about 200 m²/g. In a preferredembodiment, the active metal oxide(s) includes a yttrium oxide having aBET surface area greater than 20 m²/g, such as greater than 25 m 2/g andparticularly greater than 30 m²/g.

In one embodiment, it is preferred to utilize a catalyst compositioncomprising at least two or more metal oxides, preferably selected fromoxides of Group 2, Group 3 (including Lanthanide and Actinide seriesmetals) and Group 4 metals. The metal oxides useful in the invention arecombinable in many ways to form the active mixed metal oxides. In anembodiment, the metal oxides are mixed together in a slurry or hydratedstate or in a substantially dry or dried state. Preferably the metaloxides are contacted in a hydrated state.

In a preferred embodiment, the active mixed metal oxides can beconsidered as having atomic level mixing of the Group 2, Group 3, and/orGroup 4 metals within the oxide, in which the atomic level mixing isachieved during synthesis of the mixed metal oxide.

The active metal oxide(s) used herein can be prepared using a variety ofmethods. It is preferable that the active metal oxide is made from ametal oxide precursor, preferably a Group 2 metal salt precursor, aGroup 3 metal salt precursor, and/or a Group 4 metal salt precursor.Other suitable sources of the metal oxides include compounds that formthese metal oxides during calcination, such as oxychlorides andnitrates. Alkoxides are also sources of the metal oxides, for examplezirconium n-propoxide.

In one embodiment, the active metal oxide(s) used herein ishydrothermally treated under conditions that include a temperature of atleast 80° C., preferably at least 100° C. The hydrothermal treatmenttypically takes place in a sealed vessel at greater than atmosphericpressure. However, a preferred mode of treatment involves the use of anopen vessel under reflux conditions. Agitation of the hydrated metaloxide in a liquid medium, for example, by the action of refluxing liquidand/or stirring, promotes the effective interaction of the hydratedoxide with the liquid medium. The duration of the contact of thehydrated oxide with the liquid medium is conveniently at least 1 hour,such as at least 8 hours. The liquid medium for this treatment typicallyhas a pH of about 6 or greater, such as 8 or greater. Non-limitingexamples of suitable liquid media include water, hydroxide solutions(including hydroxides of NH₄ ⁺, Na⁺, K⁺, Mg²⁺, and Ca²⁺), carbonate andbicarbonate solutions (including carbonates and bicarbonates of NH₄ ⁺,Na⁺, K⁺, Mg²⁺, and Ca²⁺), pyridine and its derivatives, andalkyl/hydroxylamines.

In one embodiment, where the active metal oxide(s) used herein consistsof two or more oxides selected from Groups 2, 3, and 4, the active mixedmetal oxide may be prepared by impregnation of a precursor to a secondoxide onto a preformed oxide. In an alternative embodiment, the firstformed oxide may be hydrothermally treated prior to impregnation. Forexample, a Group 3/Group 4 mixed metal oxide can be prepared byimpregnating a hydrothermally treated hydrated oxide of the Group 4metal with an aqueous solution containing an ion of the Group 3 metal,followed by drying. In a preferred embodiment, the Group 3 metal islanthanum or yttrium. The resulting material is then calcined,preferably in an oxidizing atmosphere, at a temperature of at leastabout 400° C., such as at least about 500° C., for example from about600° C. to about 900° C., and typically from about 650° C. to about 800°C. The calcination time may be up to 48 hours, such as for about 0.5 toabout 24 hours, for example for about 1 to about 10 hours. In apractical embodiment, calcination is carried out at about 700° C. forabout 1 to about 3 hours.

In yet another embodiment, where the active metal oxide(s) used hereinconsists of two or more oxides selected from Groups 2, 3, and 4, theactive mixed metal oxide may be prepared by combining a first liquidsolution comprising a source of at least one of the Group 2, 3, or 4metals with a second liquid solution comprising a source of an ion of atleast one other Group 2, 3, or 4 metal. This combination of twosolutions takes place under conditions sufficient to causeco-precipitation of a hydrated precursor to the mixed oxide material asa solid from the liquid medium. Alternatively, the sources of the allthe anions of the Group 2, 3, and/or 4 metal oxides may be combined in asingle solution. This solution may then be subjected to conditionssufficient to cause co-precipitation of the hydrated precursor to thesolid mixed oxide material, such as by the addition of a precipitatingreagent to the solution. For example, the precipitating agent(s)preferably is a base such as sodium hydroxide or ammonium hydroxide.Water is a preferred solvent for these solutions.

The temperature at which the liquid medium(s) is maintained during theco-precipitation is typically less than about 200° C., such as in therange of from about 0° C. to about 200° C. A particular range oftemperatures for co-precipitation is from about 20° C. to about 100° C.The resulting gel is preferably then hydrothermally treated attemperatures of at least about 80° C., such as at least about 100° C.The hydrothermal treatment typically takes place in a sealed vessel atgreater than atmospheric pressure. The gel, in one embodiment, ishydrothermally treated for up to about 10 days, such as up to about 5days, for example up to about 3 days.

The hydrated precursor to the metal oxide(s) is then recovered, forexample by filtration or centrifugation, and washed and dried. Theresulting material is preferably then calcined, typically in anoxidizing atmosphere, at a temperature of at least about 400° C., suchas at least about 500° C., for example from about 600° C. to about 900°C., and conveniently from about 650° C. to about 800° C., to form theactive metal oxide or active mixed metal oxide. The calcination time istypically up to 48 hours, such as for about 0.5 to 24 hours, for examplefor about 1.0 to 10 hours. In a practical embodiment, calcination iscarried out at about 700° C. for about 1 to about 3 hours.

Catalyst Compositions and Their Production

Catalyst compositions useful herein include any one of the molecularsieves previously described and one or more of the active metal oxidesdescribed above, optionally with a binder and/or matrix materialdifferent from the active metal oxide(s). Typically, the weight ratio ofthe molecular sieve to the active metal oxide(s) in the catalystcomposition is in the range of 1:10 to 100:1, such as from 1:5 to 75:1,particularly from 1:1 to 50:1, and more particularly from 2:1 to 40:1.

There are many different binders that are useful in forming the catalystcompositions used herein. Non-limiting examples of binders that areuseful alone or in combination include various types of hydratedalumina, silicas, and/or other inorganic oxide sols. One preferredalumina containing sol is aluminum chlorhydrol. The inorganic oxide solacts like glue binding the synthesized molecular sieves and othermaterials such as the matrix together, particularly after thermaltreatment. Upon heating, the inorganic oxide sol, preferably having alow viscosity, is converted into an inorganic oxide binder component.For example, an alumina sol will convert to an aluminum oxide binderfollowing heat treatment.

Aluminum chlorhydrol, a hydroxylated aluminum based sol containing achloride counter ion, has the general formula ofAl_(m)O_(n)(OH)_(o)Cl_(p).x(H₂O) wherein m is 1 to 20, n is 1 to 8, o is5 to 40, p is 2 to 15, and x is 0 to 30. In one embodiment, the binderis Al₁₃O₄(OH)₂₄C₁₇-12(H₂O) as is described in G. M. Wolterman, et al.,Stud. Surf. Sci. and Catal., 76, pages 105-144 (1993), which is hereinincorporated by reference. In another embodiment, one or more bindersare combined with one or more other non-limiting examples of aluminamaterials such as aluminum oxyhydroxide, γ-alumina, boehmite, diaspore,and transitional aluminas such as α-alumina, β-alumina, γ-alumina,δ-alumina, ε-alumina, κ-alumina, and ρ-alumina, aluminum trihydroxide,such as gibbsite, bayerite, nordstrandite, doyelite, and mixturesthereof.

In another embodiment, the binder is an alumina sol, predominantlycomprising aluminum oxide, optionally including some silicon. In yetanother embodiment, the binder is peptized alumina made by treating analumina hydrate, such as pseudobohemite, with an acid, preferably anacid that does not contain a halogen, to prepare a sol or aluminum ionsolution. Non-limiting examples of commercially available colloidalalumina sols include Nalco 8676 available from Nalco Chemical Co.,Naperville, Ill., and Nyacol AL20DW available from Nyacol NanoTechnologies, Inc., Ashland, Massachusetts.

Where the catalyst composition contains a matrix material, this ispreferably different from the active metal oxide and any binder. Matrixmaterials are typically effective in reducing overall catalyst cost,acting as thermal sinks to assist in shielding heat from the catalystcomposition for example during regeneration, densifying the catalystcomposition, and increasing catalyst strength such as crush strength andattrition resistance.

Non-limiting examples of matrix materials include one or more non-activemetal oxides including beryllia, quartz, silica or sols, and mixturesthereof, for example silica-magnesia, silica-zirconia, silica-titania,silica-alumina and silica-alumina-thoria. In an embodiment, matrixmaterials are natural clays such as those from the families ofmontmorillonite and kaolin. These natural clays include subbentonitesand those kaolins known as, for example, Dixie, McNamee, Georgia andFlorida clays. Non-limiting examples of other matrix materials includehaloysite, kaolinite, dickite, nacrite, or anauxite. The matrixmaterial, such as a clay, may be subjected to well known modificationprocesses such as calcination and/or acid treatment and/or chemicaltreatment.

In a preferred embodiment, the matrix material is a clay or a clay-typecomposition, particularly a clay or clay-type composition having a lowiron or titania content, and most preferably the matrix material iskaolin. Kaolin has been found to form a pumpable, high solids contentslurry, to have a low fresh surface area, and to pack together easilydue to its platelet structure. A preferred average particle size of thematrix material, most preferably kaolin, is from about 0.1 μm to about0.6 μm with a D₉₀ particle size distribution of less than about 1 μm.

Where the catalyst composition contains a binder or matrix material, thecatalyst composition typically contains from about 1% to about 80%, suchas from about 5% to about 60%, and particularly from about 5% to about50%, by weight of the molecular sieve based on the total weight of thecatalyst composition.

Where the catalyst composition contains a binder and a matrix material,the weight ratio of the binder to the matrix material is typically from1:15 to 1:5, such as from 1:10 to 1:4, and particularly from 1:6 to 1:5.The amount of binder is typically from about 2% by weight to about 30%by weight, such as from about 5% by weight to about 20% by weight, andparticularly from about 7% by weight to about 15% by weight, based onthe total weight of the binder, the molecular sieve and matrix material.It has been found that a higher sieve content and lower matrix contentincreases the molecular sieve catalyst composition performance, whereasa lower sieve content and higher matrix content improves the attritionresistance of the composition.

The catalyst composition typically has a density in the range of from0.5 g/cc to 5 g/cc, such as from from 0.6 g/cc to 5 g/cc, for examplefrom 0.7 g/cc to 4 g/cc, particularly in the range of from 0.8 g/cc to 3g/cc.

In making the catalyst composition, the molecular sieve is first formedand is then physically mixed with the active metal oxide(s), preferablyin a substantially dry, dried, or calcined state. Most preferably themolecular sieve and active metal oxide(s) are physically mixed in theircalcined state. Without being bound by any particular theory, it isbelieved that intimate mixing of the molecular sieve and one or moreactive metal oxide(s) improves conversion processes using the molecularsieve composition and catalyst composition of the invention. Intimatemixing can be achieved by any method known in the art, such as mixingwith a mixer muller, drum mixer, ribbon/paddle blender, kneader, or thelike. Chemical reaction between the molecular sieve and the metaloxide(s) is unnecessary and, in general, is not preferred.

Where the catalyst composition contains a matrix and/or binder, themolecular sieve is conveniently initially formulated into a catalystprecursor with the matrix and/or binder and the active metal oxide isthen combined with the formulated precursor. The active metal oxide canbe added as unsupported particles or can be added in combination with asupport, such as a binder or matrix material. The resultant catalystcomposition can then be formed into useful shaped and sized particles bywell-known techniques such as spray drying, pelletizing, extrusion, andthe like.

Once the molecular sieve catalyst composition is formed in asubstantially dry or dried state, to further harden and/or activate theformed catalyst composition, a heat treatment such as calcination, at anelevated temperature is usually performed. Typical calcinationtemperatures are in the range from about 400° C. to about 1,000° C.,such as from about 500° C. to about 800° C., such as from about 550° C.to about 700° C. Typical calcination environments are air (which mayinclude a small amount of water vapor), nitrogen, helium, flue gas(combustion product lean in oxygen), or any combination thereof.

In a preferred embodiment, the catalyst composition is heated innitrogen at a temperature of from about 600° C. to about 700° C. Heatingis carried out for a period of time typically from 30 minutes to 15hours, such as from 1 hour to about 10 hours, for example from about 1hour to about 5 hours, and particularly from about 2 hours to about 4hours.

Oxygenate Conversion Process

The process of the invention is directed to the conversion of afeedstock containing one or more oxygenates to one or more olefin(s).Typically, the feedstock contains one or more aliphatic-containingoxygenate compounds such that the aliphatic moiety contains from 1 toabout 50 carbon atoms, such as, from 1 to 20 carbon atoms, for examplefrom 1 to 10 carbon atoms, and particularly from 1 to 4 carbon atoms.Non-limiting examples of suitable oxygenate compounds include alcohols,including straight and branched chain aliphatic alcohols and theirunsaturated counterparts, such as methanol, ethanol, n-propanol andisopropanol; alkyl ethers such as dimethyl ether, diethyl ether,methylethyl ether and di-isopropyl ether; alkyl ketones such as dimethylketone; aldehydes such as formaldehydes, dimethylcarbonate and variousacids such as acetic acid.

In a preferred embodiment of the process of the invention, the feedstockis selected from one or more of methanol, ethanol, dimethyl ether,diethyl ether or a combination thereof, more preferably methanol anddimethyl ether, and most preferably methanol.

The various feedstocks discussed above are converted in the process ofthe invention primarily into one or more olefin(s). The olefin(s)produced from the feedstock typically have from 2 to 30 carbon atoms,preferably 2 to 8 carbon 20 atoms, more preferably 2 to 6 carbon atoms,still more preferably 2 to 4 carbons atoms, and most preferably areethylene and/or propylene.

Using the catalyst composition of the invention for the conversion of afeedstock containing one or more oxygenates, the amount of olefin(s)produced based on the total weight of hydrocarbon produced is greaterthan 50 weight percent, typically greater than 60 weight percent, suchas greater than 70 weight percent, and preferably greater than 80 weightpercent. Moreover, the amount of ethylene and/or propylene producedbased on the total weight of hydrocarbon product produced is greaterthan 40 weight percent, typically greater than 50 weight percent, forexample greater than 65 weight percent, and preferably greater than 78weight percent. Typically, the amount ethylene produced in weightpercent based on the total weight of hydrocarbon product produced, isgreater than 20 weight percent, such as greater than 30 weight percent,for example greater than 35 weight percent. In addition, the amount ofpropylene produced in weight percent based on the total weight ofhydrocarbon product produced is typically greater than 20 weightpercent, such as greater than 25 weight percent, for example greaterthan 30 weight percent, and preferably greater than 35 weight percent.

In addition to the oxygenate component, such as methanol, the feedstockmay contain one or more diluent(s), which are generally non-reactive tothe feedstock or molecular sieve catalyst composition and are typicallyused to reduce the concentration of the feedstock. Non-limiting examplesof diluents include helium, argon, nitrogen, carbon monoxide, carbondioxide, water, essentially non-reactive paraffins (especially alkanessuch as methane, ethane, and propane), essentially non-reactive aromaticcompounds, and mixtures thereof. The most preferred diluents are waterand nitrogen, with water being particularly preferred.

The diluent, for example water, may be used either in a liquid or avapor form, or a combination thereof. The diluent may be either addeddirectly to the feedstock entering a reactor or added directly to thereactor, or added with the molecular sieve catalyst composition.

The present process can be conducted over a wide range of temperatures,such as in the range of from about 200° C. to about 1000° C., forexample from about 250° C. to about 800° C., including from about 250°C. to about 750° C., conveniently from about 300° C. to about 650° C.,typically from about 350° C. to about 600° C. and particularly fromabout 350° C. to about 550° C.

Similarly, the present process can be conducted over a wide range ofpressures including autogenous pressure. Typically the partial pressureof the feedstock exclusive of any diluent therein employed in theprocess is in the range of from about 0.1 kPaa to about 5 MPaa, such asfrom about 5 kPaa to about 1 MPaa, and conveniently from about 20 kPaato about 500 kPaa.

The weight hourly space velocity (WHSV), defined as the total weight offeedstock excluding any diluents per hour per weight of molecular sievein the catalyst composition, typically ranges from about 0.1 hr⁻¹ toabout 500 hr⁻¹, such as from about 1 hr⁻¹ to about 100 hr⁻¹, for examplefrom about 1 hr⁻¹ to about 25 hr⁻¹.

During the conversion process of the invention, carbonaceous deposits,generally referred to as “coke”, are deposited in and/or on themolecular sieve catalysts composition. Although the presence of smallamounts of coke may be advantageous in enhancing the ethylene and/orpropylene selectivity of the catalyst, the activity of the catalystdecreases rapidly if the coke levels become too high. Accordingly, thecatalyst must periodically be regenerated to burn-off some or all of thecoke on the catalyst. Regeneration is effected by contacting the cokedcatalyst composition with a regeneration medium, preferably a gascontaining oxygen, under conventional regeneration conditions oftemperature and pressure.

Non-limiting examples of suitable regeneration media include one or moreof oxygen, O₃, SO₃, N₂O, NO, NO₂, N₂O₅, air, air diluted with nitrogenor carbon dioxide, oxygen and water (U.S. Pat. No. 6,245,703), carbonmonoxide and/or hydrogen. Suitable regeneration conditions are thosecapable of burning coke from the coked catalyst composition, preferablyto a level less than 0.5 weight percent based on the total weight of thecoked molecular sieve catalyst composition entering the regenerationsystem. For example, the regeneration temperature may be in the range offrom about 200° C. to about 1500° C., such as from about 300° C. toabout 1000° C., for example from about 450° C. to about 750° C., andconveniently from about 550° C. to 700° C. The regeneration pressure maybe in the range of from about 15 psia (103 kPaa) to about 500 psia (3448kPaa), such as from about 20 psia (138 kPaa) to about 250 psia (1724kPaa), including from about 25 psia (172 kPaa) to about 150 psia (1034kPaa), and conveniently from about 30 psia (207 kPaa) to about 60 psia(414 kPaa).

Coke levels on the catalyst composition can be measured by withdrawingthe catalyst composition from the conversion process and determining itscarbon content. Typically, the conversion process is allowed to proceeduntil the coke level on the catalyst composition reaches between about 8weight percent and about 20 weight percent, such as from about 13 weightpercent to about 18 weight percent, based on the weight of the molecularsieve. At this point, the conversion process is suspended and thecatalyst is regenerated. Typical levels of coke on the molecular sievecatalyst composition, after regeneration, are in the range of from 0.02weight percent to about 2.0 weight percent, such as from about 0.02weight percent to about 0.5 weight percent, based on the weight of themolecular sieve.

Fixed Bed Reactor System

The oxygenate conversion process of the invention is conducted in afixed bed swing reactor system including a plurality of reactors eachcontaining the catalyst composition described above. In this way, eachreactor can be sequentially rotated between an operating mode, whereinthe catalyst composition in the reactor is being contacted with theoxygenate-containing feedstock to produce olefin product, and aregeneration mode, wherein the catalyst composition is being contactedwith a regeneration medium.

In one simple embodiment, the reactor system can comprise two reactors,a main reactor A and a swing reactor S. In such an embodiment, when theswing reactor S is in its operating mode, the reactor A displaced by theswing reactor is in its regeneration mode for coke removal. After cokehas been removed from reactor A, it is returned to the operating modeand the swing reactor S is returned to the regeneration mode for cokeremoval.

Since freshly regenerated catalyst tends to result in lower ethylene andpropylene selectivities than partially coked catalyst, it may bepreferrable to return the reactor with the regenerated catalyst (cokehas been burned off) to a position in the reactor system such that theregenerated catalyst does not contact the fresh feed. One simple methodto achieve this is to use three reactors (A, B and C) in series in thereaction circuit and a swing reactor S in the regeneration circuit. Theposition of A, B and C could be fixed and the swing reactor S arrangedto move to the same position as the reactor it replaces in the reactioncircuit. A suitable configuration of valving and piping could then beused to alter the direction of flow of the reaction stream through thereactors to ensure that the regenerated catalyst does not contact thefresh feed. For example, when the A reactor is being put into theregeneration circuit for subsequent regeneration, the swing reactor Sreactor with freshly regenerated catalyst could replace reactor A in thereaction circuit. Before the displacement of the reactor A by the swingreactor S the reaction stream flow direction might be A→B→C. After thereactor S displaces the reactor A, the reaction stream flow directioncould be switched to C→B→S, i.e., the reaction stream enters the reactorseries from the C reactor and exits the reactor series through the Sreactor. Heat exchanging capability could be added to the reactors sothat the exothermic heat of the reaction is removed from each reactorfor controlling reactor temperatures. Alternatively, the effluent fromeach reactor could be passed through a heat exchanger before it isintroduced to the next reactor in the reactor series.

Operations of swing reactor systems are described in detail in U.S. Pat.Nos. 4,456,779 and 4,789,528, the entire contents of which areincorporated herein by reference.

The invention will now be more particularly described with reference tothe following Examples and the accompanying drawings.

EXAMPLE 1

Five hundred grams of ZrOCl₂.8H₂O and 84 grams of La(NO₃)₃.6H₂O weredissolved with stirring in 3.0 liters of distilled water. Anothersolution containing 260 grams of concentrated NH₄OH and 3.0 liters ofdistilled water was prepared. Both solutions were heated to 60° C. andthen combined at the rate of 50 ml/min using nozzle mixing to form thefinal mixture, a slurry. The pH of the final mixture was adjusted toapproximately 9 by the addition of concentrated ammonium hydroxide. Thisslurry was then put in a polypropylene bottle and placed in a steam box(100° C.) for 72 hours. The resulting product formed was recovered byfiltration, washed with excess water, and dried overnight at 85° C. Aportion of this product, was calcined to 700° C. in flowing air for 3hours to produce an active mixed metal oxide containing a nominal 10weight percent La (lanthanum) based on the final weight of the mixedmetal oxide and having an uptake of carbon dioxide at 100° C. of 0.085mg/m² of the mixed metal oxide.

EXAMPLE 2

The following three catalyst compositions were prepared by mixingSAPO-34 with varying quantities of the mixed metal oxide of Example 1:

-   -   (a) 30 mg of SAPO-34/20 mg of mixed metal oxide;    -   (a) 40 mg of SAPO-34/10 mg of mixed metal oxide; and    -   (a) 50 mg of SAPO-34 alone.

The resultant catalysts were tested in a fixed bed reactor in theconversion of methanol at a temperature of 475° C., a pressure of 25psig (172.4 kPag) and a methanol weight hourly space velocity (WHSV) of100 hr⁻¹. The results are shown in FIG. 1 from which it will be seenthat the catalysts containing the mixed metal oxide of Example 1 agedsignificantly more slowly than the SAPO-34 alone.

Based on the 100 w/w/hr space velocity data of FIG. 1, it is expectedthat at a reasonable methanol WHSV of 3 hr⁻¹ the methanol conversionwould start at >99 wt % and it would take more than 24 hours for theconversion to drop to 50 wt %. During this period of catalystdeactivation, a gradual increase in reactor temperature could maintainthe conversion at >90-95 wt %. With a catalyst life greater than 24hours, fixed bed reactor operating in a swing reactor regeneration (SRR)mode would be economically feasible.

EXAMPLE 3

Fifty grams of Y(NO₃)₃.6H₂O were dissolved with stirring in 500 ml ofdistilled water. The pH was adjusted to 9 by the addition ofconcentrated ammonium hydroxide. This slurry was then put inpolypropylene bottles and placed in a steambox (100° C.) for 72 hours.The product formed was recovered by filtration, washed with excesswater, and dried overnight at 85° C. A portion of the dried product wascalcined to 600° C. in flowing air for 3 hours to produce yttrium oxide(Y₂O₃) having an uptake of carbon dioxide at 100° C. of 0.25 mg/m² ofthe mixed metal oxide.

EXAMPLE 4

A catalyst composition comprising 40 mg of a SAPO-34 molecular sieve and10 mg of the yttrium oxide of Example 3 was tested in a fixed bedreactor for the conversion of methanol at a temperature of 475° C., apressure of 25 psig (172.4 kpag) and a methanol weight hourly spacevelocity of 50 hr⁻¹. The results are shown in FIG. 2 from which it willbe seen that the catalyst containing the metal oxide of Example 3 agedsignificantly more slowly than the SAPO-34 alone. The presence of themetal oxide extends the life of the catalyst sufficiently to enableoxygenate conversion to occur with a fixed bed reactor operating in aswing reactor regeneration (SRR) mode in an economically feasiblemanner.

While the present invention has been described and illustrated byreference to particular embodiments, those of ordinary skill in the artwill appreciate that the invention lends itself to variations notnecessarily illustrated herein. For this reason, reference should bemade solely to the appended claims for purposes of determining the truescope of the present invention.

1. A process for converting an oxygenate-containing feedstock into oneor more olefins in a reactor system including a plurality of fixed bedreactors each containing a catalyst composition comprising a molecularsieve and at least one metal oxide having an uptake of carbon dioxide at100° C. of at least 0.03 mg/m² of the metal oxide, wherein each reactoris sequentially rotated between at least one operating mode, wherein thecatalyst composition in the reactor is contacted with theoxygenate-containing feedstock, and a regeneration mode, wherein thecatalyst composition in the reactor is contacted with a regenerationmedium.
 2. The process of claim 1 wherein said metal oxide has an uptakeof carbon dioxide at 100° C. of at least 0.035 mg/m² of the metal oxide.3. The process of claim 1 wherein said metal oxide has an uptake ofcarbon dioxide at 100° C. of about 0.04 to about 5 mg/m² of the metaloxide.
 4. The process of claim 1 wherein said metal oxide has a surfacearea greater than 10 m 2/g.
 5. The process of claim 1 wherein saidcatalyst composition also includes at least one of a binder and a matrixmaterial different from said metal oxide.
 6. The process of claim 1wherein said catalyst composition also includes a binder and a matrixmaterial each being different from one another and from said metaloxide.
 7. The process of claim 6 wherein the binder is an alumina soland the matrix material is a clay.
 8. The process of claim 1 wherein themetal of said at least one metal oxide is selected from Group 2 metals,Group 3 metals, Lanthanide series metals, Actinide series metals, andGroup 4 metals of the Periodic Table of Elements.
 9. The process ofclaim 8 wherein said metal oxide is selected from zirconium oxide,magnesium oxide, calcium oxide, barium oxide, lanthanum oxide, yttriumoxide, scandium oxide, cerium oxide, and mixtures thereof.
 10. Theprocess of claim 1 wherein the weight ratio of the molecular sieve tometal oxide is in the range of from 1:10 to 100:1.
 11. The process ofclaim 1 wherein the molecular sieve has a pore diameter less than 6Angstrom.
 12. The process of claim 1 wherein the molecular sievecomprises a framework including at least two tetrahedral units selectedfrom [SiO₄], [AlO₄] and [PO₄] units.
 13. The process of claim 12 whereinthe molecular sieve comprises a silicoaluminophosphate.
 14. The processof claim 12 wherein the molecular sieve comprises a CHA framework-typemolecular sieve.
 15. The process of claim 12 wherein the molecular sievefurther comprises an AEI framework-type molecular sieve.
 16. The processof claim 1 wherein each reactor is maintained in said at least oneoperating mode until the coke level on the catalyst composition reachesbetween about 8 weight percent and about 20 weight percent, based on theweight of the molecular sieve.
 17. The process of claim 1 wherein eachreactor is maintained in said at least one operating mode until the cokelevel on the catalyst composition reaches between about 13 weightpercent and about 18 weight percent, based on the weight of themolecular sieve.
 18. The process of claim 1 wherein each reactor ismaintained in said regeneration mode until the coke level on thecatalyst composition decreases to between about 0.02 weight percent andabout 2.0 weight percent, based on the weight of the molecular sieve.19. The process of claim 1 wherein each reactor is maintained in saidregeneration mode until the coke level on the catalyst compositiondecreases to between about 0.02 weight percent and about 0.5 weightpercent, based on the weight of the molecular sieve.
 20. The process ofclaim 1 wherein the reactor system comprises at least three of saidfixed bed reactors and each reactor is sequentially rotated from saidregeneration mode to a first operating mode, then to at least a secondoperating mode and then back to said regeneration mode, wherein reactorsin said first and second operating modes are connected in series suchthat the oxygenate-containing feedstock contacts the catalystcomposition in a reactor in the second operating mode before contactingthe catalyst composition in a reactor in the first operating mode. 21.The process of claim 1 wherein the oxygenate-containing feedstockcomprises methanol, ethanol, dimethyl ether, diethyl ether or acombination thereof.
 22. The process of claim 1 wherein, in said atleast one operating mode, the catalyst composition is contacted with theoxygenate-containing feedstock at a temperature of about 200° C. toabout 1000° C. a pressure of about 0.1 kPaa to about 5 Mpaa and a weighthourly space velocity (WHSV) of about 0.1 hr⁻¹ to about 500 hr^(−1.) 23.The process of claim 1 wherein, in said regeneration mode, the catalystcomposition is contacted with the regeneration medium at a temperatureof about 200° C. to about 1500° C. and a pressure of about 15 psia (103kPaa) to about 500 psia (3448 kPaa).
 24. A process for converting anoxygenate-containing feedstock into one or more olefins in a reactorsystem including a plurality of fixed bed reactors each containing acatalyst composition comprising a molecular sieve and at least one metaloxide having an uptake of carbon dioxide at 100° C. of at least 0.03mg/m² of the metal oxide, wherein each reactor is sequentially rotatedbetween a plurality of operating modes, wherein the catalyst compositionin the reactor is contacted with the oxygenate-containing feedstock toproduce said one or more olefins and generate coke on the catalystcomposition, and a regeneration mode, wherein the catalyst compositionin the reactor is contacted with a regeneration medium, the processcomprising connecting said reactors in said operating modes in seriessuch that the feedstock contacts the most heavily-coked catalyst firstand contacts the newly regenerated catalyst last.